Install the content compiler as a dotnet tool

The compiler that CI uses to gate and bake mesh content — the same code path the portals compile with at runtime — can now be installed directly:

dotnet tool install -g MeshWeaver.Compiler.Cli
mw-compiler <checkout-root> --bake-output <dir>
mw-compiler --print-framework-identity

A content repository's CI installs the tool version matching its platform, compiles its node trees, and publishes prebuilt-assembly bundles the portals adopt at boot instead of recompiling. The framework build identity resolves from the manifest packed inside the tool, so what the tool bakes and what a portal would accept can never disagree. The same binary also ships as the existing mw-plugin-test container image for docker-based pipelines.